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Abstract

One of the most promising avenues to perform numerical evolutions in theories
beyond General Relativity is the fixing-the-equations approach, a proposal in
which new ``driver'' equations are added to the evolution equations in a way
that allows for stable numerical evolutions. In this direction, we extend the
numerical relativity code SpECTRE to evolve a ``fixed'' version of scalar
Gauss-Bonnet theory in the decoupling limit, a phenomenologically interesting
theory that allows for hairy black hole solutions in vacuum. We focus on
isolated black hole systems both with and without linear and angular momentum,
and propose a new driver equation to improve the recovery of such stationary
solutions. We demonstrate the effectiveness of the latter by numerically
evolving black holes that undergo spontaneous scalarization using different
driver equations. Finally, we evaluate the accuracy of the obtained solutions
by comparing with the original unaltered theory.